In many end use applications, water soluble polymers are received and initially handled by users as powders which are subsequently dissolved into various water-based systems. This, however, presents a technical challenge as water soluble polymer powders tend to lump when added to water-based systems. The problem arises from rapid hydration and swelling of the water soluble polymer powders upon addition to water-based systems. When water soluble polymer powders are added in bulk, particles of the water soluble polymer at the interface between powder phase and fluid phase begin to rapidly hydrate and swell. The swelling of water soluble polymer particles at the interface and the resulting particle jamming slows down fluid penetration into the interior of the powder phase. This process ultimately results in the creation of persistent, slowly dissolving gel agglomerates of various sizes. The formation of said agglomerates in addition to slowing down the rate of water soluble polymer dissolution, also results in the presence of undesired matter in one's formulation.
A number of approaches are known in the art that have been used in producing lump free dissolution of water soluble polymers. Among the commonly-used approaches are (a) slow addition of water soluble polymer powder, (b) pre-wetting of the water soluble polymer powders with water miscible solvent, and (c) blending the water soluble polymer powder with other dry material prior to utilization. Each of the above mentioned approaches has a downside. For example, approach (a) greatly slows down powder utilization, approaches (b) and (c) may carry over substantial concentrations of additives which may have negative effects on the product to which the water soluble polymer product was added from either an environmental compliance or a performance standpoint.
Another approach used in suppressing lump formation during dissolution is based on using high shear induction equipment. In this approach, the water soluble polymer powder/water system mixtures are subjected to high shear that mechanically breaks lumps formed by the hydrating water soluble polymer powder into individual polymer particles. The shortcoming of this approach is that it requires dedicated equipment at the point of use.
A number of approaches, based on physical or chemical modification of water soluble polymer powders, have also been developed in order to attempt to provide for lump free dissolution of water soluble polymers. For example, U.S. Pat. No. 6,197,100 teaches the use of surfactants which when coated onto particle surfaces make the coated particles more easily dispersible. Patent application US2007/0175361A teaches a method of preparation of dispersible water soluble polymers by means of spray drying of the water soluble polymer powders with water soluble salts or sugars or various polymers.
U.S. Pat. No. 2,879,268 teaches a method for improving dispersibility of powders by means of chemical modification of powder surface. The patent teaches the use of formaldehyde or dialdehydes to produce surface cross-linking which allows particle dispersion prior to its solubilization.
U.S. Pat. No. 6,639,066 B2 teaches the use of blended glyoxalated cellulose ethers with various electrolytic salts. The dry blends are taught to be suitable for preparing stable suspensions by adding the dry blends to water in a single step.
U.S. Pat. No. 4,720,303 teaches the use of blends of cellulose ethers with solid organic acids, such as citric acid, tartaric acid, oxalic acid, malonic acid and succinic acid, to produce dry blends suitable for thickening water-based systems without lump formation. However, blending cellulose ethers with solid organic acids, appear to have a detrimental effect on the cellulose ether, especially hydroxyethylcellulose. Such blends of solid organic acids and cellulose ethers exhibit a decrease in the blend's shelf stability which manifests in a decrease in the solubility of the polymer.
The need exists for an approach for suppressing lump formation of water soluble cellulose ethers during dissolution which does not require the use of specialized high shear induction equipment, or through the use of additives which are either detrimental to the ultimate end use or to the shelf life of the cellulose ether, but rather results in cellulose ether powders which are capable of rapid, lump free dissolution from a direct addition to water-based systems without the disadvantage of compromised shelf stability.